The Romans under Julius Caesar subdued the Celtic Treveranss in 58 to 50 BC. When the Roman provinces in Germany were reorganised in 16 BC, Augustus decided that Trier, then called Augusta Treverorum, should become the regional capital. From 259 to 274 Trier was the capital of the break away Gallic Empire. Later for a few years (383 - 388) it was the capital of Magnus Maximus, who ruled most of the western Empire.
The city is well known for its well-preserved Roman buildings, among them the Porta Nigra, the best preserved Roman city gate north of the Alps, a complete amphitheatre, ruins of several Roman baths, and the huge Basilica, a basilica in the original Roman sense, being the 67m-length throne hall of Roman Emperor Constantine; it is today used as a Protestant church.
Trier is the oldest seat of a Christian bishop in Germany. In the Middle Ages, the Archbishop of Trier was an important ecclesiastical prince, controlling land from the French border to the Rhine. He was also one of the seven electors of the Holy Roman Empire.
Trier is also the birthplace of the influential philosopher Karl Marx.